1. Field of the Invention
This invention relates to a magnetic brush type image developer for developing an electrostatic latent image and, in particular, to a stationary magnet/rotary cylinder type magnetic brush image developer.
2. Discussion of the Prior Art
The magnetic brush image developer was originally proposed by C. J. Young in 1957 in U.S. Pat. Nos. 2,786,439 and 2,786,440. The magnetic brush image developer uses a developing agent consisting of iron powder and a toner. A "bristle" is formed by magnetic lines of force of a magnet to thereby rub the surface of a photoconductive layer with the developing agent and thus develop the electrostatic latent image. Magnetic brush image developing devices are generally classified into rotary magnet types and fixed magnet/rotary cylinder types. This invention particularly relates to the latter type, that is, the invention has as a primary object the provision of a compact fixed magnet/rotary cylinder type magnetic brush image developer.
In general, a magnetic brush image developer of the fixed magnet/rotary cylinder type has, as shown in FIG. 1, a magnet d of rectangular cross-section mounted by a supporting member c between a pair of opposingly disposed shafts b, b' which are fixedly supported on stationary structures a, a. A cylinder e is disposed around magnet d and driven from a suitable driving means f to rotate it about magnet d. For this purpose, it is necessary to provide a sufficient space at opposite ends of the afore-mentioned supporting member c for mounting the shafts b, b'. Further, rectangular magnet d has a magnetic flux density distribution as shown by the dotted line in FIG. 3, from which it can be seen that the opposite ends have a defective rise characteristic. Therefore rectangular magnet d has a limited effective developing range, that is, magnet d has to have a relatively long length l.sub.2 in order to develop a copy sheet of A4 size whose width is represented by l. Because of these limiting factors, it has been difficult to construct a compact, fixed magnet/rotary cylinder type magnetic brush image developer.